The present invention relates generally to liners for electrically heated furnaces, and more particularly to such liners as provided by stacked cylindrical segments of ceramic material in light weight cellular form.
Generally, induction heated furnaces used in metallurgical processes such as in the melting, casting, and annealing of metals are usually constructed of a cylindrical metal shell, an annular layer of thermal insulating material next to the shell, an induction heating coil next to the thermal insulating layer, and a cylindrical liner of firebrick radially inwardly from the induction heating coil. The firebrick liners used in such furnaces are assembled in situ in the furnace by cementing together individual firebricks. These liners, especially in the upper regions thereof, are subject to considerable thermomechanical degradation during the use of the furnace and when the degradation of such liner reaches a certain level, the firebricks must be removed from the furnace and replaced with a new firebrick lining. This replacement of firebrick liners occurs on a relatively regular basis in induction furnaces and requires that a mason remove and replace the firebrick within the confines of the furnace.
In some applications of the induction furnaces, various metals utilized in the metallurgical processes would pose health problems to a worker replacing the firebrick liner in the metal-processing cavity of the furnace. For example, an induction furnace in which a radioactive material such as uranium or a uranium alloy was subjected to a metallurgical process would constitute a serious health threat to a mason working within the confines of the furnace due to the radioactive contaminants remaining on surfaces in the furnace interior including the degraded firebrick liner being replaced.
Efforts to overcome the problems associated with the use of liners formed of individual firebricks, as briefly described above, include the use of one piece or multiple-piece liners formed of fibrous ceramic material. These fiber-containing liners are relatively light and can be removed from and replaced in the furnace cavity without requiring that a worker enter the confines of the furnace. However, recent investigations have shown that the ceramic fibers used in these liners are considered to be a health hazard and that the use of such ceramic fibers as furnace liners is expected to be extensively regulated or even curtailed by legislation in the near future.